1. Field of the Invention
The present invention relates to a self servo writing method of writing a final servo signal by using a reference servo signal in a hard disk drive, and more particularly, to a method of writing a uniform final self servo signal by compensating for a non-uniform track width where a reference servo signal is written, a hard disk drive using the method, and recording medium storing the method.
2. Description of the Related Art
A hard disk drive includes a plurality of magnetic heads suspended over rotating disks. The magnetic head reads and writes information on the disk by creating and sensing magnetic fields on the disk surfaces.
Each of the magnetic heads is attached to a flexure beam in order to assembly a head gimbal assembly (HGA). The HGA is attached to an actuator arm having a voice coil combined with a magnetic assembly. The voice coil and the magnetic assembly 28 constitute a voice coil motor. The voice coil motor rotates the actuator arm to move the magnetic head across the disk surfaces.
Typically, information is stored in eccentric tracks on the disk. The voice coil motor moves the magnetic head from track to track in order to access data stored on the disk surface. Each of the tracks comprises a plurality of sectors, and each sector comprises servo fields and data fields.
A tracking servo device of the hard disk drive keeps the magnetic head following the center of the track. The tracking servo reads servo burst signals from the disk, calculates the location of the magnetic head in relation to the center of the track, and controls the voice coil motor based on the calculated location to keep the magnetic head following the center of the track.
Servo information including the servo burst signals is written on the disk by a servo writer when the hard disk drive is manufactured.
A conventional method of writing the servo information uses a mechanical pushpin. The mechanical pushpin is attached to a master actuator arm at one end and extends into the hard disk drive through a servo write slot at the other end. The master actuator arm is operated under a closed loop using a positioner and a highly accurate encoder. In addition, during the servo writing process, a clock head is directed to write a clock track onto the disk to serve as a timing reference. This servo writing process suffers from problems associated with non-repetitive run-out (NRRO), disk flutter, and motor rocking, all of which reduce the accuracy in recording. Moreover, the use of the positioner and encoder greatly increases the expense associated with the servo writing process, and reduces productivity.
In order to solve these problems, methods of offline servo writing and self servo writing have been developed.
In the offline servo writing method, each disk is servo-written using an offline servo track writer before installation into the hard disk drive assembly. On the other hand, the self servo writing method is a method of writing final servo information by tracing pre-written reference servo information. In this method, the quality of written servo information is dependent on the accuracy of the reference servo information.
Higher data volumes of the hard disk drive require a higher track density, which unavoidably reduces a track margin. Therefore, it is important to keep the width of the track uniform.
A non-uniform track width can cause various problems. A magneto-resistive (MR) head is comprised of a read head and a write head. An MR offset, in which the distance between the center of the read head and the center of the write head is varied depending on the head position on the disk, is caused. Therefore it is necessary to compensate for the position of the read head by an amount equal to the MR offset in the track, so that the read head accurately follows the track written by the write head.
To this end, when the hard disk drive is manufactured, the MR offset is measured at several positions on the disk and stored in a memory. Hard disk drive compensates the position of the read head by using the stored MR offset in a read mode. When the magnetic head is between the sampled positions, the MR offset is calculated using interpolation based on the measured MR offsets at the adjacent sampled positions. The interpolation is based on the supposition in which a track width is uniform. If the width of the track is not uniform, it cannot be done adequately to compensate the MR offset by using interpolation.
When the MR offset is measured at a track having a non-uniform width, it also cannot be done adequately to compensate MR offset because the measured MR offset is not correct.
When data is written on a track having a non-uniform width especially, a track having a narrow width than others, data written on adjacent tracks might be erased.
In order to solve these problems, the conventional method measures the width of every track on the disk, and regards tracks having non-uniform width as defect tracks.
However, as the track density increases, the time taken to measure the track width increases, and the number of defect tracks increases.